How long does the internal EEPROM of an Atmel ATmega328 last for? Let’s find out…

Updated 18/03/2013

Some time ago I published a short tutorial concerning the use of the internal EEPROM belonging to the Atmel ATmega328 (etc.) microcontroller in our various Arduino boards. Although making use of the EEPROM is certainly useful, it has a theoretical finite lifespan – according to the Atmel data sheet (download .pdf) it is 100,000 write/erase cycles.

One of my twitter followers asked me “is that 100,000 uses per address, or the entire EEPROM?” – a very good question. So in the name of wanton destruction I have devised a simple way to answer the question of EEPROM lifespan. Inspired by the Dangerous Prototypes’ Flash Destroyer, we will write the number 170 (10101010 in binary) to each EEPROM address, then read each EEPROM address to check the stored number. The process is then repeated by writing the number 85 (01010101 in binary) to each address and then checking it again. The two binary numbers were chosen to ensure each bit in an address has an equal number of state changes.

After both of the processes listed above has completed, then the whole lot repeats. The process is halted when an incorrectly stored number is read from the EEPROM – the first failure. At this point the number of cycles, start and end time data are shown on the LCD.

In this example one cycle is 1024 sequential writes then reads. One would consider the entire EEPROM to be unusable after one false read, as it would be almost impossible to keep track of individual damaged EEPROM addresses. (Then again, a sketch could run a write/read check before attempting to allocate data to the EEPROM…)

If for some reason you would like to run this process yourself, please do not do so using an Arduino Mega, or another board that has a fixed microcontroller. (Unless for some reason you are the paranoid type and need to delete some data permanently). Once again, please note that the purpose of this sketch is to basically destroy your Arduino’s EEPROM. Here is the sketch:

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/*

Arduino EEPROM killer

John Boxall - http://tronixstuff.com - May 2011

CC by-sa

Note: This sketch will destroy your Arduino's EEPROM

Do not use with Arduino boards that have non-replaceable microcontrollers

Sketch assumes DS1307 already contains current date and time

*/

#include <EEPROM.h>

#include <LiquidCrystal.h>

LiquidCrystallcd(4,5,6,7,8,9);

#include "Wire.h"

#define DS1307_I2C_ADDRESS 0x68

// all these bytes necessary for time and date data

bytesecond,minute,hour,dayOfWeek,dayOfMonth,month,year;

bytesday,smonth,ssecond,sminute,shour;

bytefday,fmonth,fsecond,fminute,fhour;

// to store number of cycles. Should be enough

longcycles=0;// maximum size is 2,147,483,647

intzz=0;

voidsetup()

{

lcd.begin(16,2);// fire up the LCD

Wire.begin();// and the I2C bus

}

// Convert normal decimal numbers to binary coded decimal

bytedecToBcd(byteval)

{

return((val/10*16)+(val%10));

}

// Convert binary coded decimal to normal decimal numbers

bytebcdToDec(byteval)

{

return((val/16*10)+(val%16));

}

// Gets the date and time from the ds1307

voidgetDateDs1307(byte*second,

byte*minute,

byte*hour,

byte*dayOfWeek,

byte*dayOfMonth,

byte*month,

byte*year)

{

// Reset the register pointer

Wire.beginTransmission(DS1307_I2C_ADDRESS);

Wire.write(0);

Wire.endTransmission();

Wire.requestFrom(DS1307_I2C_ADDRESS,7);

// A few of these need masks because certain bits are control bits

*second=bcdToDec(Wire.read()&0x7f);

*minute=bcdToDec(Wire.read());

*hour=bcdToDec(Wire.read()&0x3f);// Need to change this if 12 hour am/pm

If you are unfamiliar with the time-keeping section, please see part one of my Arduino+I2C tutorial. The LCD used was my quickie LCD shield – more information about that here. Or you could always just send the data to the serial monitor box – however you would need to leave the PC on for a loooooong time… So instead the example sat on top of an AC adaptor (wall wart) behind a couch (sofa) for a couple of months:

The only catch with running it from AC was the risk of possible power outages. We had one planned outage when our house PV system was installed, so I took a count reading before the mains was turned off, and corrected the sketch before starting it up again after the power cut. Nevertheless, here is a short video – showing the start and the final results of the test:

So there we have it, 1230163 cycles with each cycle writing and reading each individual EEPROM address. If repeating this odd experiment, your result will vary.

Well I hope someone out there found this interesting. Please refrain from sending emails or comments criticising the waste of a microcontroller – this was a one off.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.

Today we are going to examine the internal EEPROM in our Arduino boards. What is an EEPROM some of you may be saying? An EEPROM is an Electrically Erasable Programmable Read-Only Memory. It is a form of non-volatile memory that can remember things with the power being turned off, or after resetting the Arduino. The beauty of this kind of memory is that we can store data generated within a sketch on a more permanent basis.

Why would you use the internal EEPROM? For situations where data that is unique to a situation needs a more permanent home. For example, storing the unique serial number and manufacturing date of a commercial Arduino-based project – a function of the sketch could display the serial number on an LCD, or the data could be read by uploading a ‘service sketch’. Or you may need to count certain events and not allow the user to reset them – such as an odometer or operation cycle-counter.

What sort of data can be stored? Anything that can be represented as bytes of data. One byte of data is made up of eight bits of data. A bit can be either on (value 1) or off (value 0), and are perfect for representing numbers in binary form. In other words, a binary number can only uses zeros and ones to represent a value. Thus binary is also known as “base-2″, as it can only use two digits.

How can a binary number with only the use of two digits represent a larger number? It uses a lot of ones and zeros. Let’s examine a binary number, say 10101010. As this is a base-2 number, each digit represents 2 to the power of x, from x=0 onwards:

See how each digit of the binary number can represent a base-10 number. So the binary number above represents 85 in base-10 – the value 85 is the sum of the base-10 values. Another example – 11111111 in binary equals 255 in base 10.

Now each digit in that binary number uses one ‘bit’ of memory, and eight bits make a byte. Due to internal limitations of the microcontrollers in our Arduino boards, we can only store 8-bit numbers (one byte) in the EEPROM. This limits the decimal value of the number to fall between zero and 255. It is then up to you to decide how your data can be represented with that number range. Don’t let that put you off – numbers arranged in the correct way can represent almost anything!

There is one limitation to take heed of – the number of times we can read or write to the EEPROM. According to the manufacturer Atmel, the EEPROM is good for 100,000 read/write cycles (see the data sheet). One would suspect this to be a conservative estimate, however you should plan accordingly. *Update* After some experimentation, the life proved to be a lot longer…

Now we know our bits and and bytes, how many bytes can be store in our Arduino’s microcontroller? The answer varies depending on the model of microcontroller. For example:

Boards with an Atmel ATmega1280 or 2560, such as the Arduino Mega series – 4096 bytes (4 kilobytes)

Boards with an Atmel ATmega168, such as the original Arduino Lilypad, old Nano, Diecimila etc – 512 bytes.

If y0u are unsure have a look at the Arduino hardware index or ask your board supplier.

If you need more EEPROM storage than what is available with your microcontroller, consider using an external I2C EEPROM as described in the Arduino and I2C tutorial part two.

At this point we now understand what sort of data and how much can be stored in our Arduino’s EEPROM. Now it is time to put this into action. As discussed earlier, there is a finite amount of space for our data. In the following examples, we will use a typical Arduino board with the ATmega328 with 1024 bytes of EEPROM storage.

To use the EEPROM, a library is required, so use the following library in your sketches:

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#include "EEPROM.h"

The rest is very simple. To store a piece of data, we use the following function:

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EEPROM.write(a,b);

The parameter a is the position in the EEPROM to store the integer (0~255) of data b. In this example, we have 1024 bytes of memory storage, so the value of a is between 0 and 1023. To retrieve a piece of data is equally as simple, use:

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z=EEPROM.read(a);

Where z is an integer to store the data from the EEPROM position a. Now to see an example.

This sketch will create random numbers between 0 and 255, store them in the EEPROM, then retrieve and display them on the serial monitor. The variable EEsize is the upper limit of your EEPROM size, so (for example) this would be 1024 for an Arduino Uno, or 4096 for a Mega.

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// Example 31.1 - Arduino internal EEPROM demonstration

#include <EEPROM.h>

intzz;

intEEsize=1024;// size in bytes of your board's EEPROM

voidsetup()

{

Serial.begin(9600);

randomSeed(analogRead(0));

}

voidloop()

{

Serial.println("Writing random numbers...");

for(inti=0;i<EEsize;i++)

{

zz=random(255);

EEPROM.write(i,zz);

}

Serial.println();

for(inta=0;a<EEsize;a++)

{

zz=EEPROM.read(a);

Serial.print("EEPROM position: ");

Serial.print(a);

Serial.print(" contains ");

Serial.println(zz);

delay(25);

}

}

The output from the serial monitor will appear as such:

So there you have it, another useful way to store data with our Arduino systems. Although not the most exciting tutorial, it is certainly a useful.

Have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.